Radar systems are known to require the generation of high-power signals over a short time period. One method for supplying the energy for generating a high-power pulse is to retain energy in a storage capacitor, and rapidly discharge the capacitor to provide the energy necessary to generate the radar pulse. This method meets the requirement of providing high-power energy to the pulse generator over a short period of time. Variations in load current from pulse to pulse result in a varying voltage drop in the unavoidable circuit and component “parasitic” resistances lying between the voltage source and the pulse generator. In order for the pulse generator to receive a substantially constant voltage during the pulse in the presence of such resistances, it is desirable to maintain a substantially constant load, i.e., a constant number of RF (radio frequency) amplifier loads pulsed at relatively constant rates. However, as the load becomes dynamic (for example, load changes associated with waveform diversity or pulse-to-pulse frequency diversity), parasitic resistance effects between the power supply output and the storage capacitor begin to impact the pulse-to-pulse voltage applied to the capacitor, and therefore to the pulse generating transmitting amplifiers. These parasitic resistance effects arise from the resistance effects of the power supply output filter and also from bus traces leading from the power supply to the output filter, and from the output filter to the storage capacitor. Modern radar systems often use low voltage, high-power Gallium Arsenide (GaAs) Field Effect Transistor (FET) amplifiers, that typically operate with a relatively low 10 vDC drain voltage bias input. Even relatively small parasitic resistance effects can produce pulse-to-pulse voltage variations which are significant as a percentage of the bias voltage. In some cases, the parasitic resistances can result in as much as a six percent (6%) voltage variation. Voltage variations of this magnitude can cause significant degradation of radar Clutter Improvement Factor (CIF), and can have impacts on calibration. These degradations and impacts arise due to voltage-dependent phase and amplitude changes in the pulses generated by the pulse transmit amplifiers.
Numerous techniques can be used to mitigate the CIF and calibration impacts. For example, larger copper conductors (having greater cross-sectional area and consequently lower resistance) can be used. The larger conductors, and increases in the size of magnetic cores on which such conductors are wound all contribute to increases in the size and weight of the power supply, and have adverse cost impact. One known method for tending to reduce the effects of parasitic resistance is to use degenerative feedback, using a remote sensing connection of the power supply to the storage capacitor, thereby including the parasitic resistances within the feedback loop. This technique, however, undesirably tends to introduce a low frequency pole into the power control loop, which in turn negatively impacts loop roll-off and AC line frequency suppression. Linear (non-switching or dissipative) regulation at the storage capacitor or at the RF amplifier power input can regulate out the parasitic resistance effect, thereby potentially eliminating droop of the power supply output pulse applied to the radar pulse transmit amplifiers. However, such regulation has a negative impact to the size, weight, cost and efficiency of the supply. Typically, an additional ten percent (10%) power system efficiency degradation occurs when linear regulation is used with a conventional 10VDC GaAS FET transmit amplifier. Furthermore, such regulation requires the use of a relatively large number of pulses with constant pulse width and duty cycle in the coherent processing interval (CPI) to afford relatively constant average power delivery during CPI intervals.
Hence, there is a need for a power supply that provides enhanced pulse and intra-pulse voltage regulation for diverse loads and waveform requirements for radar pulse transmit amplifiers